第21题: [单项选择]It was essential that all the necessary documents ______ to the president's office before the end of this month. A. be handed in B. must be handed in C. should hand in D. had been handed in 参考答案:A 答案解析:[分析] 测试点为虚拟语气。当essential,strange, necessary,important,等形容词作主句表语时,其后接的主语从句常用“should+动词原形”构成虚拟语气。shoul